Method of spray coating using laser-energy beam

ABSTRACT

A laser-radio frequency system for generating a high temperature beam and for directing and modulating the combined beam at a workpiece or target. The system includes a hollow circular electrode mounted within a circular nozzle and spaced apart from the nozzle to define an annular gap. A radio frequency generator having a hollow metal coil as its tank coil is connected to the nozzle and a pressurized inert gas is fed through the tank coil into the nozzle. When the generator is activated, a coherent R.F. electron stream is emitted from the electrode and the inert gas flows along the annular gap to sheath and focus the stream into an energy beam directed toward the workpiece. A laser generator provides a laser beam through the hollow portion of the electrode which is reflected and focused onto the workpiece; therefore an algebraic summation of both electromagnetic energies is obtained at the workpiece in the non-oxidizing atmosphere. The radio frequency tank coil may be connected to a source of powder for spraying a coating on the workpiece.

BACKGROUND OF THE INVENTION

This is a division of application Ser. No. 409,167, filed Oct. 24, 1973,now U.S. Pat. No. 3,872,279.

This invention relates generally to electronic flames or radio frequency(R.F.) energy beams in combination with laser beams to provide an energysystem for communications, for heating and for otherwise operating onworkpieces. Much of the background of the R.F. energy beam portion ofthis invention may be found in the U.S. Pat. No. 3,648,015, issued toThomas E. Fairbairn on Mar. 7, 1972.

The R.F. energy portion of the beam, which is generally known, isgenerated by a conventional radio frequency having a tank coil in itsoutput circuit. The tank coil is a hollow metal tube into which inertgas is introduced under pressure. The output of the tank coil is coupledthrough a nozzle having an electrode mounted therein, and uponapplication of power to the radio frequency generator, an R.F. electronenergy beam is emitted from the tip of the electrode and this beam issheathed and focused by the inert gas.

Unsuccessful attempts have been made to treat certain metals with lasersprior to my invention. For example, it is not yet possible to performdeep penetration welding of aluminum with only a laser, because aluminumhas a mirror like finish, and lasers have a high index for reflectionoff of aluminum. Furthermore, the present laser welding units, to weldother metals, require lasers generating in excess of 10 kilowatts ofpower at a cost of about $50 per watt, or a total cost in excess of$500,000.

The present invention contemplates a method and apparatus for providinga composite laser-radio frequency energy beam system. Prior to myconception of this invention, it was not known that the laser beam couldbe utilized in conjunction with an R.F. plasma type energy beam.

The present invention includes a radio frequency energy beam generatorsuch as a torch, modified over the torch described in my U.S. Pat. No.3,648,015, and combined with a laser generator. The torch of the presentsystem includes a nozzle having a hollow electrode mounted therein. Thelaser beam is focused through the hollow portion of the electrode,without hitting the inner surface of the electrode, along with a lowpressure gas. The laser is focused on a workpiece such as by anadjustable Cassegranian reflector. The energy beam generator isgenerally set forth in my prior patent, and upon energization of theradio frequency generator and introduction of an inert gas, the hollowelectrode emits the coherent R.F. plasma energy beam. The R.F. plasmaenergy beam is sheathed or surrounded by an annular ring of inert gaswhich limits the scattering of the beam.

It is an object of the present invention to provide an improvedoxidation resistant energy system which has a high energy level andheats work much faster and more controllably in a unit area of a targetthan prior art systems. Because of these features, the workpiece may bemoved more rapidly through the beam for deep penetration fusion welds.

It is another object of the present invention to provide an energysystem which permits point focusing of an intense portion of thesummation of both energy beams for rapid traversing of the work,regardless of surface reflectivity of the target.

The present invention provides for a continuous beam which requires lesspeak power for deep penetration welding of metals including aluminum,and ceramics at a cost reduction of 10 times that of present lasers.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing objects of the present invention, together with otherobjects and advantages which may be attained by its use, will becomemore apparent upon reading the following detailed description taken inconjunction with the drawings.

In the drawings, wherein like reference numerals identify correspondingparts:

FIG. 1 is a diagrammatic illustration of the laser-R.F. energy beamtorch of the present invention;

FIG. 2 is an enlarged, partly sectional illustration of the nozzle andelectrode of the torch of the present invention;

FIG. 3 is an enlarged perspective partial illustration of the nozzle andelectrode of the torch of FIG. 2; and

FIG. 4 is a side elevation of the electrode as seen in the direction ofthe arrows 4--4 of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

The laser beam-radio frequency energy beam system of the presentinvention includes a radio frequency generator 10 having a conventionaloutput tank circuit 11 and a tank coil 12. The choice of the particularradio frequency generator may be made by those killed in the art as longas a coherent single frequency R.F. sine wave is the output. Anexemplary circuit is shown in my U.S. Pat. No. 3,648,015 which is herebyincorporated by reference. The tank coil is a hollow copper tubing bothends of which are electrically and mechanically connected to the tankcircuit as at 13.

In addition to the electrical input to the tank coil 12 supplied by theR.F. generator 10, there is a pressurized fluid input provided from afluid supply 14. The fluid may be water or may be a gaseous media suchas oxygen, propane or hydrogen, or other inert gas. An inert gas such asair or helium is preferred. A fluid path is defined from a tube 16through a T-fitting 18 and a supply tube 20 to a low voltage, highcurrent point on the tank coil 12. Inert gas under very low pressure isintroduced at a low voltage point of the tank coil to prevent ionizationof the gas with its resultant effect upon the fittings and the tank coilsuch as shorting, melting and the like.

A powder material or other aggregate may also be introduced into thetank coil for spraying onto a workpiece, from a supply of powder 22. Thepowder or aggregate supply 22, together with a carrier gas 24, aresupplied as inputs to a secont T-fitting 26. The output of thisT-fitting goes through a tube 28 to the T-fitting 18. Thus, the powdersupply, which is optional, is also introduced into a low voltage, highcurrent point of the tank coil 12 and is conveyed in a smaller tube, notshown, within the tube or tank coil 12.

The output from the tank coil is taken at a high voltage, low currentpoint through a tube 30 to an electrically conductive nozzle 32. Thisprovides the radio frequency input to the nozzle.

The laser input is provided by a pair of Q-switched laser amplifiers,such as Sylvania's 4A8-CO₂ type, including a first amplifier 34 and asecond amplifier 36. These are high power amplifiers which are aligned,as is conventional, to provide a laser beam which is introduced into therear of the nozzle 32, such as through a focusing lens 38.

The hollow nozzle 32, which has an outlet orifice 33, includes anelectrode 40 having a main body 41 with a hollow center 42. The nozzlehas a curved front face which may be highly polished to serve as amirror as at 44. The electrode is mounted within and electricallyconnected to the nozzle by three threaded screws 46 spaced 120° apartand projecting radially inwardly towards the hollow center of theelectrode. The three threaded screws 46 provide a force fit on the outersurface of the electrode and the space between the electrode and thenozzle defines an annular air gap 48. The length of the electrode mayextend past the nozzle orifice and may be adjusted by first releasingthe screws 46 to focus the elctron beam.

The electrode 40 also includes an extension or ring 50 which is attachedto the main body 41 of the electrode by a plurality of electricallyconductive struts or supports 52. The extension 50 also has a hollowcenter 54 and has a rear surface mirror 56 facing the main body 41 and afront surface or electrode tip 58.

A workpiece 60 is positioned a distance away from the electrode tip 58to receive both the laser beam and the electron plasma beam.

Upon energization of the radio frequency generator 10 and uponapplication of the inert gas, the coherent R.F. electron-plasma energybeam is generated. Although the nozzle 32 and the electode tip 58 remaincool, the tip 58 emits a high frequency coherent electron-plasma energystream and the inert gas which passes through the annular air gap 48between the electrode body 41 and the nozzle 32 forms an annular sheathwhich limits the outward scattering of the stream and directs andfocuses it into a beam which annular sheath flows around the extension50 and impinges onto the workpiece. The energy beam goes through thehollow center 54 of the extension and is emitted from the tip 58. TheR.F. beam will take a relatively long time to melt the workpiece (one tothree) seconds compared to a focused laser beam.

To provide an improved energy absorption, the laser beam is combinedwith the R.F. energy beam. The laser beam output of the Q-switched laseramplifiers proceeds on a straight path through the lens 38, continuesthrough an opening 68 in the end of the body 41, through the hollowcenter 42 of the electrode 40 and is then reflected back off the rearface 56 of the electrode extension. The reflected laser beam is againreflected off the curved face 44 of the nozzle 32 onto the workpiece 60.Both the rear 56 of the extension 50 and the curved face 44 are highlypolished to reflect the laser beam. Thus they operate as a Cassegranianreflector system and still allow the inert gas to pass through the holeor aperture 54.

The front face or tip 58 of the electrode extension 50 is typicallymolybdenum, tungsten or platinum.

The struts 52 are threaded into the curved face 44 so that the electrodeextension 50 may be moved axially toward or away from the workpiece toadjust the focal point 62 where the laser beam impinges upon theworkpiece.

The laser beam provides a high energy beam which serves as an energyguide for the R.F. energy beam which, in turn, is readily absorbed bythe workpiece. The combined effect of the laser beam and radio frequencyenergy beam is similar to the operation of a drill bit with the laserbeam operating similar to a feed screw to "penetrate" or initiatemelting of the workpiece and with the R.F. electron being operated asthe "cut-lip" of the blade to melt additional material.

If it is desired to spray a powder or aggregate fusing or coating ontothe workpiece, this may be accomplished by activating the powder oraggregate supply 22 and its associated carrier gas 24 as set forth inthe aforementioned patent. The powder follows a second tube which iswound within the tank coil 12 and which emerges from the tube 30 as atube 64 external to the nozzle (FIG. 1) or as a tube 66 internal to thenozzle (FIG. 2), through a window or aperture 67. Optionally, the inertcarrier gas may always be "on" with the aggregate 22 introduced throughfitting 26 when desired. It is preferred to have gas "on" through innerand outer tubes 66 and 30 whether or not powder is being sprayed, toprovide for laminar flow of the gas and improved beam control.

The use of the laser beam serves to heat, by ionization and other means,the inert gas as it emerges from ring electrode 50 during operation andthus the gas reaches the surface of the workpiece at higher temperatureand higher energy peaks than in the prior art.

The helium, air, or inert gas emerging from the hollow center 42 of theelectrode and passing through the hole 54 in the extension 50 conductsthe R.F. coherent sine wave energy to the workpiece. The helium isionized partially by the laser beam as it travel through the hollowelectrode. This partially ionized gas stream does not fully ionize untilit emerges through the electrode extension 50 which is where the R.F.energy is supplied to fully generate the R.F. energy beam from theelectrode tip 58.

The R.F. energy E, will also modulate the laser energy E₂ (carrier).Both waves are electromagnetic and the algebraic sum and difference forenergy apply. Thus, using Planck's constant, E_(T) =hv, where V =frequency, and E_(T) = E₁ + E₂ (algebraic).

It should be appreciated that the purpose of the lens 38 is to focus thelaser beam and prevent the laser from damaging the inside walls of thehollow electrode body 41. Thus this lens is not necessary and only awindow is needed if the amplifier is provided with a suitable focusingmechanism.

Similarly, the electrode extension or ring 50 of the Cassegranian typemirror or reflector system may be a hollow mirror or lens with atungsten facing to define the electrode tip 58.

Thus the foregoing is a description of one embodiment of the presentinvention and should not be construed in a limiting sense but only asdescribing the underlying concepts involved. The invention should belimited only by the scope of the following claims.

What is claimed is:
 1. In a method for spraying a coating on a workpiecewith a high temperature coherent electromagnetic beam emitted from anorifice, by generating a single frequency sine wave signal in a hollowelectrically conductive tubular tank coil of a radio-frequencygenerator; injecting an inert gas and a heat fusable material in acarrier gas into a maximum current-low voltage point of said tank coil;convey said inert gas and said material in its carrier gas separatelythrough said coil to an exit port located at a maximum voltagelow-current point of said coil; conveying said inert gas from said exitport through a hollow electrically conductive outlet tube to a nozzlehaving an outlet orifice; conveying said material from said exit port tosaid nozzle orifice; transmitting said single frequency sine wave signalfrom said maximum voltage low-current point of said coil around a hollowelectrode means centrally located in said nozzle orifice, whilemaintaining said electrode means and said surrounding nozzle at the sameelectrical potential; the improvement characterized by generating alaser beam; conveying said laser beam through said outlet nozzle andthrough the hollow portion of said electrode means; and reflecting saidlaser beam from the hollow portion of said electrode means onto saidworkpiece and focusing the laser beam thereon; whereby said inert gasforms an annular sheath which surrounds and focuses into a beam the hightemperature coherent radio-frequency-plasma electron stream emitted fromsaid electrode means and nozzle orifice and said material enters thebeam thus emitted and is sprayed onto said workpiece with the energy insaid beam causing the material to be fused on the workpiece as acoating.